The temporomandibular joints (TMJs) connect the jaw to the skull and generate large amounts of force in the jaw. In between these two bones rests a fibrocartilagenous disc termed the TMJ meniscus, which acts to disperse the forces on the jaw and reduce friction during movement. In anatomy, a meniscus is a fibrocartilagenous structure present, e.g., in the knee, acromioclavicular, and sternoclavicular joints that, in contrast to articular discs, only partly divides a joint cavity.
The TMJs are unusual because they are one of the only synovial joints in the human body comprising a disc meniscus. The disc separates the lower joint compartment formed by the mandible and the articular disc (allowing rotational movement) from the upper joint compartment (allowing translational movements). The top of the mandible which mates to the under-surface of the disc is termed the “condyle” and the temporal bone of the skull that mates to the upper surface of the disk is termed the “glenoid (or mandibular) fossa.” The TMJ meniscus differs substantially from other meniscuses such as the knee meniscus, as it comprises almost entirely type I collagen as opposed to approximately 80% type I/20% type II collagen in the knee. Temporomandibular joint disorder or dysfunction (TMD) occurs when there is pain at or near the temporomandibular joint. Broadly, TMD comprises a group of disorders involving the joints, muscles, tendons, ligaments, and blood vessels at the joint. One type of disorder of the TMJ is internal derangement (ID), which involves an abnormality of the meniscus-temporal fossa relationship, resulting in a mechanical disorder that creates irregular joint noises and prohibits normal condylar movement. Although the etiology remains obscure, various inflammatory mediators have been implicated. For example, synovial fluid analysis indicates a role of cytokines and proteinases in development of ID. Moreover, interleukins have been detected in both ID and rheumatoid arthritis of the TMJ. One possible mechanism is the inducing release of proteinases and collagenases by inflammatory cytokines. Despite this understanding, treatment for such derangement is usually surgical.
For example, internal derangement due to ankylosis, meniscal perforation, and degenerative joint disease, among others, can be treated by a meniscectomy Complications arising from meniscectomy without replacement include heterotopic bone formation and joint ankylosis. The rationale for replacing the TMJ meniscus with a substitute material is to protect the articular surfaces from further degenerative changes and to avoid joint adhesion formation. Many alloplastic materials such as SILASTIC™, silicone and PROPLAST™-Teflon, have been used to replace the TMJ meniscus but results have been less than satisfactory. Often times, joint pathology is more severe following the placement of such devices. Autograft tissues have been used both as disc replacement materials following meniscectomy and as interpositional materials in the treatment of joint ankylosis. Sources such as the temporalis muscle flap, auricular cartilage, and dermis have proven far better options than their alloplastic counterparts but still have the obvious disadvantage of morbidity associated with the graft donor site. Furthermore, a variety of studies have shown fibrosis or, in the case of the temporalis muscle flap, necrosis and devitalization of autogenous tissue grafts.
Thus, what is needed is a graft material for the treatment of TMJ pathology with associated meniscus abnormality is a scaffold for cellular influx and that would be readily implanted without the associated morbidity of autogenous tissue harvest. It is also desirable that the graft closely match the natural state of the disc which is hypovascular, aneural, and alymphatic while being able to function mechanically immediately after implantation.